This scheme is used to prevent the opening of the non-load break disconnect switches while the breaker is closed; insuring the disconnect switches are locked open and the breaker isolated by the removal of and evidence/hold-off key, or using the evidence/hold-off key for testing/servicing of the breaker.
Initial Condition: The load bus is fed from line bus through non-load break disconnect switch #1, breaker #1, and switch #2. Switch #1 is locked closed with no interlock key present in its LC position key interlock. Switch #1 has a "B" key captive in it's LO position key interlock. Switch #2 is locked closed with no interlock key present in its LC position key interlock, switch #2 has a evidence/hold-off key captive in its LO position key interlock. Breaker #1 is closed with its respective interlock key "A" captive.
Opening the non-load break disconnect switches thereby isolating breaker #1: Open and lock breaker #1 thereby releasing the "A" key. Use the "A" key to unlock and open switch #1. Lock switch #1 in the open position thereby removing the "B" key. Use the "B" key to unlock and open switch #2. Lock switch #2 in the open position thereby releasing the evidence key. Supervisory personnel may hold this key as evidence of the switching operation, or to re-close breaker #1 for testing/servicing. Reverse to restore the initial condition.
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